Eastern grey kangaroos Macropus giganteus are gregarious, with females mostly philopatric and most males dispersing.  Females are thus assumed to form kin clusters but details of associations among different sex-age classes in this species are largely unknown.  We observed 153 marked kangaroos at Wilsons Promontory National Park, Australia.  We examined relationships within and between six different sex-age classes using half-weight indices and lagged association rates.  We found subtle social structure.  Mean half-weight indices were similar within compared to between different sex-age combinations.  For adult females, there was a weakly positive relationship between pairwise relatedness and dyadic half-weight indices but this effect disappeared after controlling for geographic distance or spatial overlap.  Lagged association rates decreased exponentially only for adult males with adult females accompanied by young-at-foot in the breeding season.  Most other lagged association rates decreased slightly in a linear fashion and few were constant.  Although females without young-at-foot appeared to be more social than females with young-at foot, all associations among individuals were weak.  Contrary to expectations, the social structure of kangaroos was not based on female relatedness at high density under strong fission-fusion dynamics.